Peroxiredoxins (Prxs) are expressed in the epidermis, and the accentuated expression of the Prx I and Prx II isotypes (Prx I/II) in the suprabasal layers suggests the potential role of Prx I/II in epidermal differentiation. To evaluate the novel function of Prx I/II, we checked the modulation of Prx I/II in differentiating keratinocytes. To induce differentiation in vitro, normal human epidermal keratinocytes (NHEK) were cultured for up to 10 days after the confluent state (post-confluency). In Western blot analysis, the marked induction of Prx I was observed from the second day, but the marked induction of Prx II was observed later from the sixth day of post-confluency, when loricrin and transglutaminase 1 were induced (sixth day of post-confluency). When NHEK cells were treated with INF-gamma and TGF-beta1, Prx I/II were up-regulated by INF-gamma, but Prx I/II were down-regulated by TGF-beta1. In summary, Prx I and Prx II are induced at the early and late stage of differentiation of NHEK cells, respectively.